Determining the events associated with the processing, transport, localization, storage, and translation of a mRNA are critical to our overall understanding of when, where, and how much of a protein is synthesized. In recent years the pivotal role of the 3' untranslated region (3' UTR) of the mRNA in affecting these facets of mRNA behavior has been amply demonstrated. For example, during mammalian spermatogenesis, the Prm-1 gene is first transcribed shortly after meiosis in round spermatids, however, its mRNA is not translated until up to a week later in elongating spermatids. The study of fusion genes in transgenic mice has shown that the cis-acting sequence elements required for Prm-1 translational repression map within the 3' UTR of the mRNA. The next advance in the understanding of how 3' UTRs mediate their diverse effects on mRNA will require the identification of the trans-acting factors that interact with the 3' UTRs and that link them to other molecules in the cell. The broad goals of our research are to identify genes involved in controlling the various aspects of mRNA behavior described above, and to investigate the mechanisms by which they function during mammalian germ cell development. Specifically, in this proposal we intend to: 1) Determine the consequences of premature translation of Prm-1 mRNA during the early haploid stages of spermatogenesis in transgenic mice. 2) Clone the gene for a germ cell-specific protein that binds to the 3' UTRs of the mouse Prm-1 and Prm-2 mRNAs. 3) Create and analyze a mutation in the Prbp gene in transgenic mice. Create a series of mutations in the Prm-1 3' UTR and assay them for Prbp binding in vitro. Create and analyze two Prbp binding site-mutations in vivo. Knowledge gained from these studies may ultimately contribute to our understanding of some causes of male infertility, to the inheritance of genetic diseases, and to the development of a male contraceptive.